Don't let the current node be chosen as synchronous (#3112)

It could happen that there is "something" streaming from the current primary node with `application_name` that matches name of the current primary, for instance due to a faulty configuration. When processing `pg_stat_replication` we only checked that the `application_name` matches with the name one of the member nodes, but we forgot to exclude our own name.
As a result there were following side-effects:
1. The current primary could be declared as a synchronous node.
2. As a result of [1] it wasn't possible to do a switchover.
3. During shutdown the current primary was waiting for itself to release it from synchronous nodes.

Close #3111

tests/test_sync.py

@@ -98,3 +98,20 @@ class TestSync(BaseTestPostgresql):
         self.s.set_synchronous_standby_names(CaseInsensitiveSet('*'))
         mock_reload.assert_called()
         self.assertEqual(value_in_conf(), "synchronous_standby_names = '*'")
+
+    @patch.object(Postgresql, 'last_operation', Mock(return_value=1))
+    def test_do_not_prick_yourself(self):
+        self.p.name = self.leadermem.name
+        cluster = Cluster(True, None, self.leader, 0, [self.me, self.other, self.leadermem], None,
+                          SyncState(0, self.me.name, self.leadermem.name), None, None, None)
+
+        pg_stat_replication = [
+            {'pid': 100, 'application_name': self.leadermem.name, 'sync_state': 'sync', 'flush_lsn': 1},
+            {'pid': 101, 'application_name': self.me.name, 'sync_state': 'async', 'flush_lsn': 2},
+            {'pid': 102, 'application_name': self.other.name, 'sync_state': 'async', 'flush_lsn': 2}]
+
+        # Faulty case, application_name of the current primary is in synchronous_standby_names and in
+        # the pg_stat_replication. We need to check that primary is not selected as the synchronous node.
+        with patch.object(Postgresql, "_cluster_info_state_get", side_effect=[self.leadermem.name,
+                                                                              'on', pg_stat_replication]):
+            self.assertEqual(self.s.current_state(cluster), (CaseInsensitiveSet([self.me.name]), CaseInsensitiveSet()))